The present invention relates to drive systems, and particularly to variable speed drive systems. More particularly, the invention relates to variable speed drive systems for use with self-propelled, walk-behind devices such as lawn mowers.
In a single speed self-propelled lawn mower, the engine is generally indirectly coupled to a set of drive wheels to propel the lawn mower at a single speed, which is usually related to the engine speed. Typically, a drive pulley is mounted to an output shaft of the engine and a belt or other transmission mechanism connects the drive pulley to a drive shaft which in turn rotates the drive wheels. When the drive system is engaged, the lawn mower automatically assumes the single speed. When the drive system is disengaged, the lawn mower stops.
If any variable speed control exists, it is typically accomplished by changing the engine speed. Unfortunately, this can be disadvantageous in situations where the operator might prefer a higher engine speed and a lower lawn mower speed, such as when cutting tall grass. If the engine speed is increased to provide for increased speed of the cutting elements and better cutting, the lawn mower moves faster and thereby negates the benefit of the increased speed of the cutting elements. Moreover, for some people, the single speed may be too fast or too slow and, therefore, an uncomfortable speed for walking behind a lawn mower. A variable speed mechanism that would allow the operator to adjust the speed of the lawn mower to suit the individual needs of the operator and separately control engine speed would be an improvement over conventional single speed drive systems.
Variable speed drives for use with self-propelled lawn mowers are known. See, for example, U.S. Pat. No. 2,740,246 to Smith et al., U.S. Pat. No. 3,015,237 to Musgrave, and U.S. Pat. No. 4,117,652 to Jones et al.
In variable speed, self-propelled lawn mowers, two separate mechanisms are generally used to operate the lawn mower. An engagement mechanism is actuated to engage the drive system to begin propelling the lawn mower and a separate speed control mechanism is utilized to adjust the speed of the lawn mower. Moreover, conventional variable speed drive systems utilize complex and costly multiple gear sets or friction drive wheels and a clutch. A variable speed drive system that eliminates the complex and costly mechanisms yet uses a single mechanism to set the desired speed and to engage the drive system would provide a substantial improvement over conventional drive systems in the form of reduced manufacturing costs and maintenance requirements.
A mechanism that would allow any operator to preset a personally comfortable lawn mower speed to be automatically assumed when the drive system is engaged would be advantageous. Such a drive system that also allowed for temporarily reducing the speed as necessary, for instance to move around obstacles or the like, would further improve conventional self-propelled lawn mower drive systems.
The present invention provides a variable speed drive system for use with a self propelled device having an engine mounted to a frame and a pair of drive wheels coupled to a drive shaft for propelling the lawn mower. The system includes a variable pitch pulley that is coupled by a belt to a drive pulley mounted on an output shaft of the engine. The variable pitch pulley is coupled to the drive shaft by a chain housing fixture. The fixture positions the pulley in spaced-apart relation to the drive shaft, and moves about the drive shaft between an engaged position and a disengaged position.
In the disengaged position, the belt connecting the drive pulley to the variable pitch pulley is slack and does not drive the variable pitch pulley. Moving the fixture about the drive shaft toward an engaged position removes the slack from the belt connecting the drive pulley to the variable pitch pulley. As the fixture is moved further toward the fully engaged position, tension in the belt urges the belt radially inwardly toward the center of the variable pitch pulley. As the pitch of the pulley changes in response to the inward movement of the belt, the effective radius of the variable pitch pulley decreases, thereby increasing the speed of rotation of the variable pitch pulley relative to the drive pulley. Thus, the pitch of the pulley changes in response to movement of the fixture about the drive shaft and the speed of the self-propelled device changes in response to the changes in the pitch of the variable pitch pulley. Consequently, moving the fixture about the drive shaft directly changes the speed of the lawn mower.
The variable pitch pulley is connected to a drive sprocket and the drive shaft is connected to a driven sprocket. An endless chain engages the drive sprocket and the driven sprocket while the fixture retains the drive sprocket and driven sprocket in spaced-apart relation to each other. The fixture includes a clam shell housing for enclosing the chain and the sprockets while maintaining the drive sprocket and the driven sprocket in spaced-apart relation to each other.
The self-propelled device also has a handle, with an engagement bail coupled thereto, and a bracket mounted to the frame and positioned in space-apart relation to the fixture. The bail is movable between an engaged position adjacent the handle and a disengaged position. The bail is connected by a spring and cable to the fixture so that movement of the bail toward the engaged position moves the fixture and variable pitch pulley about the drive shaft toward the engaged position.
A speed control lever, also coupled to the handle, is positioned to allow an operator to limit the amount of movement of the cable in response to movement of the bail to the engaged position. Limiting the amount of movement of the cable directly limits the amount of movement of the variable pitch pulley and the fixture about the drive shaft and therefore limits the speed of the self-propelled device. A spring connected to the cable and to the bail extends as necessary to allow the cable to stop at any desired position while permitting the bail to reach the engaged position.
The cable connecting the bail to the fixture is surrounded by, and longitudinally movable through, an outer cable housing. In one embodiment of the invention, one end of the outer housing is attached to the bracket and the other end is attached to the handle. According to one aspect of the invention, the speed control lever interferes with a stopper formed on the cable to limit the amount of cable movement available in response to movement of the bail toward the engaged position. When the speed control lever interferes with the stopper, the cable stops moving. The spring extends to allow the bail to move any remaining distance to the engaged position. Since the speed of the self-propelled device is directly related to the amount of movement of the variable pitch pulley and the fixture about the drive shaft, limiting the amount of movement of the cable directly determines the maximum speed of the lawn mower by limiting the amount of fixture movement about the drive shaft in response to movement of the bail to the engaged position.
In another embodiment of the invention, one end of outer cable housing is attached to the bracket and the second end is coupled to the speed control lever. Moving the speed control lever repositions the second end of the outer cable housing and therefore determines the amount of cable movement available in response to movement of the bail to the engaged position. Thus, when the second end of the outer housing is moved toward the bail, there is some movement of the bail before the bail applies tension to the cable, and the bail reaches the engaged position before the maximum cable runout is achieved. With less cable runout in response to the movement of the bail to the engaged position, the fixture moves less than the full amount about the drive shaft and a less than maximum speed is achieved.
When the second end of the outer housing is moved away from the bail, an increased amount of cable movement is available in response to movement of the bail to the engaged position. Tension is applied to the cable as soon as the bail begins to move. The maximum amount of cable runout is achieved at some point before the bail reaches the engaged position, and the spring deforms to allow the bail to reach the engaged position. Full runout of the cable in response to movement of the bail to the engaged position provides full movement of the fixture about the drive shaft and thus maximum speed is achieved. Since the speed of the self-propelled device is directly related to the amount of movement of the variable pitch pulley and the fixture about the drive shaft, the positioning of the outer housing determines the maximum speed of the self-propelled device by determining the amount of cable movement (and therefore fixture movement) available in response to movement of the bail to the engaged position.
Additional objects, features, and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of a preferred embodiment exemplifying the best mode of carrying out the invention as presently perceived.